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Revenue (Summary of Type of Customer, Contract Revenues) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax $ 589,625 $ 648,781 $ 726,149
Foreign [Member]      
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax   149 6,596
Type of Customer [Member] | Operating Segment [Member]      
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax 589,625 648,781 726,149
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member]      
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax 586,962 648,781 726,149
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | Federal Government [Member]      
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax 438,790 431,705 568,980
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | State and Local Government [Member]      
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax 129,583 207,033 118,712
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | Private [Member]      
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax 18,589 9,894 31,861
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | Foreign [Member]      
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax   $ 149 $ 6,596
Type of Customer [Member] | Operating Segment [Member] | Offshore Wind [Member]      
Disaggregation Of Revenue [Line Items]      
Revenue from Contract with Customer, Excluding Assessed Tax $ 2,663